Ignition system



Aug. 10, 1948. H. w. SHERIDAN ETA.

IGNITION SYSTEM Filed March 22, 1943 I N VEN TORS fmm Sheridan Mme/rdfb/[ By n Af tyf Patented Aug. 10, 1948 IGNITION SYSTEBI mnmw.Sheridan. osk'ruk, and wmen o. Taylor, Chicago. Ill.

Application March 22, 1943, Serial No. 479.964

1. claim. 1

This invention relates to ignition mechanism for use in internalcombustion engines, and the like.

One of the objects of the invention is the provision of new and improvedignition mechanism that has a maximum of efllciency and that occupies aminimum amount of space.

A further object of the invention is the provision of a new and improvedignition mechanism so constructed as to eliminate corona cutting,thereby adding to the effectiveness of the ignition sparks delivered bythe spark plugs for igniting the charges in the engine cylinders.

A further object of the invention is the provision of a new and improvedspark plug assembly comprising an electric interruptor, and atransformer detachably mounted on a spark plug and so 'constructed andarranged as to form a unitary structure therewith.

A still further object of the .invention is the provision of a new andimproved high tension system of ignition for internal combustion enginesthat is simple in construction, easily assembled. eillcient inoperation, and that eliminates the necessity for conducting high tensioncurrents over extended conductors.

Other and further objects and advantages of the invention will appearfrom the following description taken in connection with the accompanyingdrawings, in which f Fig. 1 is a wiring diagram illustrating oneapplication of the invention into the sparkplugs of an internalcombustion engine;

Fig. 2 is a vertical section of aspark plug, shown more or lessdiagrammatically; and Fig. 3 is an exploded view of the spark plusshowing the same in perspective.

A great amount of trouble has been experienced in the operation ofairplane engines, especially those that ascend to extremely highaltitudes, It

has been found that the insulation for the high l tension wires rapidlydeteriorates, resulting in misflring of the charges in the cylinders andnot infrequently in stoppage of one or more of the engines. This is dueto corona cutting of the insulation. There is often considerable loss ofelectrical energy from high tension wires, and this loss increases asthe pressure of air on the insulation decreases. This loss oftenmanifests itself in a halo or corona about the high tension conductors,The escaping energy ionizes the air, and the continued bombardment ofthe insulation by these ionized particles in time perforates theinsulation and renders it ineffective.

'I'he present invention seeks to eliminate this 2 dilculty by the use ofwhat-will be termed a low tension ignition system. That is, the lowvoltage will not be transformed to a higher voltage adjacent the sourceof the current, as is the present practice. but will be transformed intohigher voltages adjacent its point of application which, in an ignitionsystem, will be adjacent to the spark plugs. By means of thisarrangement the high tension voltages may be well protected, and thehigh tension conductors will be of minimum length, thus entirelyobviating any danger of corona cutting of the insulation. Furthermore,the transformer is so mounted that it is not affected by atmosphericconditions during its use.

Referring now to the drawing, the reference character IIl indicatesdiagrammatcally the system as applied to an internal combustion engineII, having a plurality oi' cylinders I2 each provided with a spark plugassembly I3 extending into the combustion chamber Il of each cylinder.For illustrative purposes the engine is shown with only four cylinders.It is understood that in the use of airplanes, the more expensiveautomobiles. and the like. a larger number of cylinders are employed,but since the principle is` the same it is not thought necessary tocomplicate the drawing by disclosing additional cylinders.

As is ,usual in internal combustion engines of the compression type,each cylinder is provided with a spark plug having a spark gap acrosswhich an electric spark is caused to jump for igniting the charge at theproper stage of its compression. A suitable source I5 of electriccurrent, such as a magneto or storage battery, is employed forenergizing the system. The source Ilmay be grounded, as at I8, on thecar or plane, and a lead I1 is adapted to conduct the current to adistributor I8, as is usual in such constructions. The distributor Il isprovided with a conductor arm Il. which is adapted to be rotated tobring the sameinto successive engagement with the contact members 2|,which are insulated from each other and which in turn are electricallyconnected with corresponding spark plugs I3, as by means of the leads22.

The current passing from the source I5 will explode the chargesintermittently in a predetermined orderin the cylinders, in the usualmanner. The order of firing is not shown in the drawing, because it isnot believed necessary to an understanding of the invention, and inorder to avoid confusion of lines the exact order of firing is notindicated.

Suitable means are provided for converting the low tension current fromthe source I5 into a high tension one before it reaches the firing sparkgap on the lower end oi' the spark plug assembly it. In Ethe form ciinvention selected to illustrate one embodiment thereof, an interrupteri3 and transformer it are employed for this purpose, and these areclosely associated with the central electrode oi the spark plug. Thespark plug assembly lil is preferably, though not necessarily,sectional, and comprises the upper section or interrupter les, theintermediate section or transformer i311, and the lower section or sparkplug l3. This lower section 0r spark plug comprises a metallic shell ormetallic .member 2li, screw-threaded at its lower end, as at 2B, forenfl gaging a corresponding threaded opening in the cylinder head. It isscrew-threaded at its upper end, as at 25, for engaging a clamping nut,as will presently appear. This plug is provided with integral hexagonalshoulders or sides '2lb for receiving a wrench for attaching the plug tothe engine cylinder. The interior of the plug has an axial opening 2lwhich, in the form shown, tapers toward its lower end. The lower end ofthe plug is apertured to form a truncated cone 28 for receiving acorrespondingly shaped insulating plate or plates 29, as will presentlyappear.

The plug is provided with a suitable central electrode 3i, the lower endof which is provided with an annular shoulder 32 on which an insulatingplate 29 is adapted to seat. The electrode 3| is also suitably insulatedfrom the metallic portion or shell 23 of the plug, and its lower endcooperates with a terminal 20 on the shell for forming a spark gap forthe plug. As shown, a sleeve of mica 33, or other insulating temperatureresisting material, is provided which surrounds the electrode, andsurrounding the sleeve 33 is a stack of apertured insulating plates 34ofmica or other insulating and heat resisting elements. Extending acrossthe uppe` end of the column or stack 34 of insulating plates is anenlarged plate 35 of mica or other suitable insulating heat resistingmaterial, which rests on the upper ilat face of the spark plug, as shownmore clearly in Fig. 2 of the drawing.

The plug or insulating plate 29 is tapered to correspond with the taper28 of the lower end of the opening through the plug. and the parts areheld iirmly in assembled relation by a nut 36 threaded :on the upperscrew-threaded end of the central electrode 3l. In order that the partsmay be :held rmly in position, a metallic plate 3l is placed beneath thenut 35, and the nut is tightened up for bringing the plug 29 iirmly intothe [conical opening 23, thus forming a gas-tight joint at this point.By tapering the plug 29 upwardly the force of the explosion will tend totighten the plug and thus maintain a gas-tight joint. 'Ihe plate 31extends across the opening 2l, and its outer' edge overlaps the walls ofthe plug, thus enabling the nut 36 to be firmly screwed down on theterminal for holding the parts in assembled relation. A

In order to reduce corona cutting to a minimum, it is desirable that the.means for transforming the low tension current from the source l5 intoa high tension current be adjacent to the spark plug, so as to reducethe length of the high tension conductors. and in the --form ofconstruction shown means are provided whereby it is mounted on andbecomes a unitary structure with the plug I3. It has been found that amore satisfactory spark is obtained if a vacuum tube be employed in theprimary circuit,- the vacuum prising two terminals or contacts that arenormaliy together but are adapted for separation in response to currentow therefor to break the primary circuit. The voltage developed in asecondary at the moment an interrupter breaks the circuit in a primarywill depend on the promptness oi the collapse of the magnetic held atthe time of the interruption. This in turn is aected by the suddennessor celerity with which the circuit is opened, that is, the time elapsingduring the circuit opening operation and the absence of ionized gasenveloping the gap. The use of a solenoid as a circuit breaker is moreprompt and sudden in its operation than is possible with a cam-operatedinterrupter. Furthermore, since there is no gas, or very little, in avacuum type oi interrupter, ionization is not present, and hence thebreak in the circuit is instantaneous with a consequent sudden collapseof the magnetic field and a resulting tremendously high voltage spark inthe spark plug. By using a vacuum interrupter the transformer may bemuch smaller in size. In fact it may be small enough, in an ignitionsystem, to be mounted on the spark. plug and carried thereby, and yetdevelop a very high tension at the spark plug gap.

In order to facilitate assembly and removal of the parts, theinterrupter 38 is built as a complete unit, and the transformer 39 isconstructed also as a separate unit; and the parts are so arranged thatthey may all be assembled with the spark plug as one unitaryconstruction,

The circuit interrupter comprises essentially al container 4l, having areduced upper portion or neck 42, in the form oi? a closed containerlhaving the air evacuated therefrom. 'I'his container may be of glass orother suitable material. In the construction shown a glass bulb,somewhat like a light bulb, is employed within which the interruptermechanism is mounted and the air,

or practically all of it, is exhausted. The air is so rare Within thebulb that the space will, for convenience of description, be referred.to herein as a vacuum. A circuit breaker is provided within this vacuumcontainer, and this circuit breaker is automaticallyIelectromagnetically operated. The switch comprises a pair of terminals43 and 44. The lower terminal 43 is iixed on a suitable support 45,which also is a conductor, as will presently appear. The upper terminal4t is carried by a rod 46, the upper end of which constitutes themovable member ill of a solenoid.

The solenoid 4l is held normally in lowered position by a lightcompression spring dt, operating between the solenoid and the upper wallof the reduced portion or neck d2 of the container 4l. An electromagnet49 surrounds the neck 42, and, when energized, causes the solenoid 4l tobe elevated, thus breaking the circuit between the contact members 43and 44. The rod 46 is positioned within the container 4I by means of oneor more c-shaped spring rod members 5I, which are extremely light andresilient.

The solenoid 41, springs 48, 5I, and contact member 44 are all verylight, so that they have but little inertia. These parts are assembledin the container 4l, the air exhausted, and the container sealed. 1 Theinterrupter may be, and preferably is, assembled in a suitable casing 52of metal or plastic material, which is adapted to be detachably securedtothe transformer 33 by suitable .bolts 53 extending through the casingand threaded into suitable internallythreaded sockets |54 secured in theupper wall of the housing for tube having therein a. gap-forming meanscomthe transformer, as will presently appear. A gasket Il may beinserted between `the casing 52 and the top wall of the transformerhousing for sealing the casing 52, if desired. The conductor 45 of thelower contact member 43 extends to the exterior of the casing Il, andterminates in a button lli. A conductor 55 is adapted to be connected tothe conductor 45 or button I0, as by being welded thereto in anysuitable manner.

The casing 52 may be in the form of an inverted cup, as shown in Fig. 1,and this cup, after the interrupter is assembled therein, is adapted tobe filled with some suitable insulating material 'which is plastic atvery high temperature.

only, but will not be seriously affected by the temperatures to whichthe interrupter is subjected. This material may be of any of thecommercial types of heat resisting compositions that is plastic at hightemperatures, such as the compositions which have ground mica as a basewith a temperature resisting binder, such as. the resins of high meltingpoints. The container 52 has an axialvopening in its top wall throughwhich a terminal 58 extends. This terminal is insulated from thecontainer wall by a suitable insulation, such as the eyelet 51, which issealed in position. A binding nut 58 is provided for attaching the outerend of the conductor 22 thereto. One end of the winding for theelectromagnet 49 is att-ached to the terminal-post, as at 58, and theother end 6| of this winding is connected to the spring member 5l" whichconstitutes a conductor for the circuit of the low tension system.

The transformer unit 39 may be, and preferably is, located between thespark plug 26 and interrupter 38, and is mounted on the spark plug. Thetransformer comprises a core 62, a primary winding about the core, 63,and a secondary windi118 84 which extends about the primary winding.

The turns of the transformer are merely indicated, there being many morethan here shown. The number of turns are such that the voltage of thesparking current may be that desired, which is usually several thousandvolts. The transformer is enclosed in an inverted cup-like container 88,of metal or other material impervious to air, having an axial opening 65in its upper wall in which an eyelet 68 is secured, and through whichthe lead 55, connected with one end of the primary windlng, extends.This lead is sealed against the passage of air.

The container 68 is preferably of metal and the primary is groundedthereon, as at 61. The lower end of the cup-shaped member or housing 68is flanged outwardly, as shown at 59, and is adapted to seat on theouter edge of the insulator block 35. A closure plate 69, having aconcave central portion 69h, is welded to the flange 68 to form anair-tight transformer unit. The flange 69 is held rmly against the blockby the ange 19 of a flanged nut 1I, which engages the threads 25on theupper end of the spark plug for clamping the parts firmly in position.The

a suitable insulating material, such as the commercialinsulating'composition of ground mica 'and a binder of resin of highmelting point, which housing 38 may be, and preferably is, lled with 6it is used on airplanes and the like. It will thus be seen that when theparts are assembled a plug is provided that is not affected by airpressure at any altitude, and that since the transformer is in closeproximity to the plug there is no likelihood of stoppage of the enginecaused by corona cutting and variation in atmospheric pressure on thevarious parts. One end of the secondary is grounded on the casing 68, asat 61, and the other end is extended to form a lead 73 which is securedto the central electrode 3| of the plug, as by being welded thereto.

Should the spark plug become disarranged or broken, or fail for anyreason, al1 that is necessary is to release the nut 1|, break theconnec- `tion between the lead 'I3 and the electrode 3|, re-

connect the lead with' the electrode of the new sparkv plug, and tightenthe nut 'Il of the new plug. Likewise, either the interrupter unit 38 orthe transformer unit 39 may be replaced, if necessary.

It is thought from the foregoing, taken in connection with theaccompanyin" drawings, that the construction` and operation my devicewill be apparent to those skilled in the art, and that changes in size,shape, proportion or detail may be made without departing from thespirit and scope of the appended claim.

We claim as our invention:

In a device of the "class described, .a transformer unit for a sparkplug comprising a container, a primary and a secondary coil sealedwithin said container, said container being filled with an insulatingcomposition for insulating the turns of said coils from one another,means for mounting said transformer unit on said spark plug and aninterrupter unit mounted on said transformer unit, saidy interrupterunit including a vacuum chamber, a conductor extending through saidchamber, and electrically operated means within said chamber for openingand closing a circuit through said conductor, said con-4 ductor being incircuit with said primary.

The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 580,988 Moore Apr. 20, 1897604,686 Moore May 24, 1898 754,666 Miller Mar. 15, 1904 945,278 LincolnJan. 4, 1910 1,017,300 Lincoln Feb. 13, 1912 1,036,760 Wilcox Aug. 27,1912 1,200,592 Cunningham Oct. 10, 1916 1,207,193 Mason Dec. 5, 19161,302,308 Cavanaugh Apr. 29, 1919 1,393,866 Whisler Oct. 18, 19211,415,581 Kratz et a1 May 9, 1922 1,554,649 Perrem Sept. 22, 19251,624,951 Holthouse Apr. 19, 1927 2,112,214 Tognola Mar` 22, 19382,121,607 McIlvaine June 21, 1938 .2,131,483 Ringwald Sept. 27, 19382,180,358 Hooven Nov.`21, 1939 ,2,232,881 Larson Feb. 25, 1941 2,258,810Rabezzana Oct. 14, 1941 Rose Dec. 19, 1944

